Astaxanthin (trans 3,3'-dihydroxy-4,4'-diketo-.beta..beta.'-carotene also known as trans 3,3'-dihydroxy-.beta.,.beta.'-carotene-4,4'-dione) is an oxycarotenoid pigment widely distributed in plants and animals. It is a predominant oxycarotenoid pigment in crustaceans, and salmonids. Astaxanthin is also found in algae, yeast (such as Phaffia rhodozyma), bacteria and birds.
In commercial aquaculture it is desirable to add astaxanthin to the diet of salmonids and crustaceans to impart the distinctive pink coloration found in indigenous salmonids, crustaceans and birds. Imparting this distinctive pink coloration to salmonids and crustaceans produced by commercial aquaculture is believed to be important in encouraging consumer acceptance of salmonids and crustaceans produced through aquaculture. Currently no economical source for astaxanthin exists.
One potential source of aztaxanthin for aquacultural purposes is the yeast Phaffia rhodozyma. Phaffia rhodozyma has been recognized, since its classification as a yeast species having a high astaxanthin content (.about.85% of its carotenoid pigment is astaxanthin, N. W. Miller, et al. Int. J. Syst. Bacteriol., Vol. 26, p. 286 (1976). Use of this yeast as a dietary supplement in salmonid and crustacean diets has also been explored by Eric A. Johnson and other researchers since the early 1980's.
The development of Phaffia rhodozyma as a commercial source of astaxanthin has been hampered by the absence of strains of Phaffia rhodozyma which produce high levels of astaxanthin. The strains of Phaffia rhodozyma currently available generally produce from 30 to 2000 micrograms per gram of cell mass. Unfortunately the strains of Phaffia rhodozyma which are high astaxanthin producer exhibit extremely slow growth rates which render them unsuitable for commercial fermentation. Thus, it would be very advantageous to develop strains of Phaffia rhodozyma which produce high levels of astaxanthin and desirable growth rates (thereby providing higher overall yields).
Unfortunately the only method currently available for improving Phaffia rhodozyma strains is through repeated rounds of mutagenesis. However, repeated rounds of mutagenesis produces Phaffia rhodozyma strains with numerous mutations deleterious to the commercial fermentation of these strains. Thus improving Phaffia rhodozyma strains becomes increasingly difficult with each successive round of mutagenesis. This problem cannot be solved by utilizing classical mating techniques because sexual reproduction is unknown in Phaffia rhodozyma. Spheroplast fusion techniques could offer an alternative to classical mating techniques as a method for improving Phaffia strains, if a technique could be developed to generate Phaffia rhodozyma spheroplasts. However, Phaffia rhodozyma has an incredibly tough cell wall which has prevented researchers from being able to produce Phaffia spheroplasts suitable for cell fusions.
Thus, it would be advantageous to develop new strains of Phaffia rhodozyma which produce higher yields of astaxanthin.
It would also be advantageous to develop a process to produce Phaffia rhodozyma spheroplasts suitable for use in cell fusions.
It would further be useful to develop a process for fusing spheroplasts of Phaffia rhodozyma.
Thus it is an object of the present invention to provide strains of Phaffia rhodozyma which produce high yields of astaxanthin.
It is a further object of the present invention to provide a process for producing Phaffia rhodozyma spheroplasts suitable for use in cell fusions.
It is yet another object of the present invention to provide a process for fusing spheroplasts of Phaffia rhodozyma.
Other aspects, objects and several advantages of this invention will be apparent from the instant specification.